The present invention concerns an improved landing gear for an aircraft. More particularly, but not exclusively, this invention is concerned with landing gear suitable for use with composite wings. The invention also concerns a method of retracting a landing gear.
The primary loads experienced by a landing gear during normal operations are typically categorised as vertical loads, drag loads and lateral loads. Typically, vertical loads act along an axis parallel to the vertical axis of the aircraft and are generated by the action of gravity on the mass of the aircraft, particularly during landing. Drag loads act along an axis substantially parallel to the longitudinal axis of the aircraft and are generated by friction between the tyres and ground on ‘spin up’ of the wheels at touchdown and also when braking. Lateral loads act along an axis substantially parallel to the lateral axis of the aircraft and are generated during steering. The landing gear may also be subject to secondary loads such as torque loads and aerodynamic drag.
In certain aircraft the main landing gear is mounted on the wing. The wing structure must have sufficient strength to react the landing gear loads at the point or points to which the landing gear attaches. This may limit the choice of materials that can be used in construction and/or lead to the need for the structure to be reinforced, thereby increasing the weight of the aircraft. This is a particular issue for wings using composite materials, for example Carbon Fibre Reinforced Polymer (CFRP) wings, as these materials are typically anisotropic. For example, CFRP materials can withstand higher loading along the fibre length, but may require substantial reinforcement to accommodate off-axis loads. It would therefore be desirable to provide a landing gear that results in an improved load profile, for example a reduction in the maximum load experienced at the point(s) of attachment to the wing and/or a reduction in off-axis loads.
One prior art method of reducing the loads experienced at any one point of attachment is to provide a landing gear which transfers loads from the landing gear to the aircraft over multiple attachment points including points on both the wing and the fuselage. EP 0 031 602 describes such a landing gear. However, many of those designs provide a very uneven load distribution across the multiple attachment points, with the majority of the load still being carried via one or two attachment points and/or with significant loads still being transferred from the landing gear to the wing. Accordingly, it would be advantageous to provide a landing gear with an improved load distribution.
Typically, modern landing gear are retracted once the aircraft is in flight. Space is at a premium within the envelope of the aircraft and accordingly it is desirable that a landing gear can be retracted into a compact configuration. However, many multiple attachment point landing gears are not particularly compact when retracted and/or are mechanically complex thereby increasing manufacture and/or maintenance costs. It would be advantageous to provide a mechanically simple landing gear that can transfer a significant proportion of the landing gear loads to the fuselage of the aircraft while maintaining a compact configuration when retracted.
The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved landing gear.